1. Technical Field
The present invention relates to a clamp including a swivel function for connecting a surface crossing or a subsurface buoy to a six twined anchoring line (steel wire) which most often is used for anchoring floating off-shore units. The clamp comprises a clamping means consisting of two halves split in the longitudinal direction of the wire to clamp around the wire.
2. Background of the Invention
In the following description, line and steel wire are used in parallel. The steel wire is that typically used for anchoring floating off-shore units.
Wire clamps are used for connecting floating elements (buoys) to lift anchoring lines above hinder on the sea bottom, such as a pipeline, or other submarine construction. The buoys can further be used for locally reducing the weight of a line.
Certain off-shore units will be anchored using 8 to 12 wire lines (2 to 3 lines in each corner of the unit) connected in their opposite ends to an anchor. The diameter of the lines varies commonly from about 64 mm to 90 mm and the length is typically about 2000 to 2300 m.
As these units often are moved between different positions, it means that different crossing points between the line and different pipelines occur. It becomes necessary to be able to attach, in a simple way, floating elements to the line in order to lift it above the crossing point without damaging or splitting the same.
When the line is subject to different tensile strengths, the line may be torn due to torsion forces. The lines vary in diameter and connected length. It is also very important that the buoy joint to the line itself does not move its position along the line.
An anchoring line costs about 500,000 to 700,000 crowns (SEK) and thus it is of utmost importance that the buoy attachment does not damage the line. Damages can occur from pure wear but also by means of exhaustion if the construction is not completely reliable.
The object of the present invention is to obtain a buoy attachment solving the above mentioned problems and simultaneously fulfills all above mentioned requirements in a simple and rational way.
These problems can be overcome by means of the present invention. A clamping mechanism includes two semicircular segments. When the clamping mechanism is positioned around a wire, an inner space is formed. The inner space is filled with an insert molded from polyurethane for locking the clamp in an axially and rotationally fixed relationship with respect to the wire. The clamp means is provided with a sliding surface for a schackle being rotatably arranged around the clamp means which swivel forms a fastening point for a ramification line.
The two segments of the clamping mechanism are typically made from steel and have inlets and outlets formed as trumpet nozzles. They are coated with a thin layer (about 5 mm) of a polyurethane which is further formed with a unique impression of the steel wire.
The bending radiuses of the steel halves laid together (of the trumpet nozzles) shall never be less than 9 times the diameter of the line in order to avoid exhaustion damages of the line.
The imprint of the steel wire which is preferably placed in the center of each steel half has a length of about 500 mm in order to allow a simple mounting but simultaneously achieve a high longitudinal retaining force. If the imprint is made longer, the mounting of the wire clamp is made more difficult as the diameter of the lines varies somewhat along the length thereof.
The hardness of the polyurethane layer arranged upon the steel halves must be flexible, have a high retention force, and admit a simple mounting. A hardness corresponding to A-95 of the standards given has seemed to be suitable.
In order to absorb the rotation of the line where the outer part with the inbuilt schackle constructed with an over measure.
As the size of the floating element varies and large dynamic forces can develop in the buoy line it is required that a high strength schackle is used. For a 76 mm anchoring line, a schackle having the mark SWL 85 Tonnes is normally used, which has been adapted by manufacturing and thereby degraded to a SWL 50 Tonnes schackle. Using a normal security factor of 5, a tensile strength of at least 200 Tonnes (200,000 kg) is achieved. Also specially designed schackles having the right geometry will be used.
The two steel halves are further so constructed that a clamping force is always achieved at different loads in the line as they do not completely circumference the whole periphery of the line.